of new bocheixe



S. RUBEN RESISTANCE DEVICE May 2, 1933.

Filed Oct. 6, 1980 Original FiIed Oct. 6, 1930 8 INVENTO'R BY ATTORNEYSAMUEL RUBEN {Reissued May 2,1933

UNITED STATES PATENT OFFICE $AMUEL RUBEN, OF NEW ROCHELLE, NEW YORK,ASSIGNOR TO RUBEN PATENTS COM- PANY, OF NEW ROCHELLE, NEW YORK, ACORPORATION .OF DELAWARE RESISTANCE DEVICE Original No. 1,859,344, datedMay 24, 1932, Serial No. 486,698, filed October 6, 1930. Application forreissue filed October 22, 1932. Serial No. 639,127."

This invention relates to a resistance device. It specifically relatesto a variable resistance device which employs copper compounds as theresistance element. The ob- 5 ject of the invention is the provision ofa variable resistance device capable of permanent operation and having awide range of resistance within predetermined limits.

For certain applications the invention constitutes an improvement uponthe variable resistance device described in my co-pending application306,608filed in the United States Patent Oflice September 17, 1928, bymeans of which contact pressure changes vary the conductivity of acuprous oxide resistance element.

In variable resistance elements of the prior art Various materials areemployed,such as a coating .upon a ceramic base, composed of a thinlayer of carbon, tellurium, graphite or germanium. To obtain widerranges of re-. sistance variation, other means are used, such asmultiple coatings upon sections of the element.

coating of any of thesematerials, employing the usual hinder materials,such for instance, as sodium silicate, the resistance layers are subjectto atmospheric efl'ects andiare not permanent. Accurate control isdifficult to obtain, as is uniformity of product.

I have found that copper oxidized at a temperature so high as to form apure cuprous oxide mass, having its crystals thermally fused ito a clearruby red material, produces a permanent high resistance body.

I have also found that if such cuprous oxide body is exposed tothe'vapors of ammonium polysulphide the oxide is converted into cuproussulphide and its resistance decreases in proportion to the period ofexposure and the density of the vapor. For example, a solid strip ofcuprous oxide three inches by one inch by twenty-fiye mils, has aresistance of about 500,000 ohms. As a contact is moved along towardsthe more completely converted region, the resistance of the, stripdecreases with the length included in the circuit. After being suspendedvertically over a quantity of ammonium polysulphide, it is partiallyBecause of the inherent weakness of a thin Y converted into cuproussulphide, the degree of conversion'being dependent upon the proximity ofthe area of the surface of the sulphide and the time of exposure. Byexposure of the cuprous oxide element to the heated vapors of seleniumor tellurium, the oxide is converted into a selenide or telluride havinglow resistance. That is, after such treatment the resistance change isgreatest at a section exposed where the vapor density was greatest andleast at a point most remote from the surface of the sulphide. Thus, theoxide strip which had 500,000 ohms resistance over its three inchlength, and indirect proportion to the distance between contacts, nowhas a high resistance at one end and a low resistance at the other, thelatter dependent on the percentage of V oxide converted to sulphide. Theresistance of another strip so treated varied somewhat in the followingorder: 1st quarter (exposed longest to the sulphide vapors), 500 ohms;2nd, 2,000 ohms; 3rd, 20,000 ohms; 4th, 50,000 ohms. The ratio varieswith the time and temperature of the exposure and with the shape of thecopper compound body. lVhen applied to a circular piece, such as used inrotary type of resistance or potentiometer, different sectionalresistance values are obtained by exposing portions of the oxide stripto the sulphide vapor for diiierent lengths of time. Thus a rotaryresistance has been made having a resistance range of 100 ohms to100,000 ohms within 270 of a slider contact. The oxide and sulphidesections are hard and of smooth crystalline material and are capable oflong use.

To more completely describe this invention, reference is made to theaccompanying drawing of one embodiment thereof, in which Fig. 1 shows aplan view of one side of the device and Fig. 2 a sectional view at 22.

'In the drawing 1 indicatesa solid cuprous oxide circular strip mountedon porcelain 'base 2 and having terminals at 3 and 4. At

5 is an arm mounting contact brush spring 6, rotating on metal rod 7 andhaving a terminal at 8. Knob 9 is mounted on rod 7 for rotating thecontact arm, the contact brush 6 being held in contact with resistancestrip 1, by nut 10 against spring 11.

The resistance strip is made by heating a copper piece of the desiredshape in an oxidizing atmosphere at approximately 1030 G. for two hourswhen the copper is wholly converted into a vitreous mass of cuprousoxide. This temperature is necessary to insure conversion of any cupricoxide that may 1 be formed during the heating into cuprous oxide and toproduce a fused-like structure.

The surface of the element is then composed When thus cleaned, the stripconstitutes a chemically pure cuprous oxide element of a bright ruby redcolor and which is translucent. Sections of the oxide strip are thenexposed to vapors from ammonium polysulphide for different periods,according to the desired resistance range or control. The resultantresistance element consists of a base of cuprous oxide, coated with alayer of much higher conductivity, consisting of a mixture of copperoxide and copper sulphide, the proportion of copper sulphide in thislever varying along the length of the resistance. For a low, resistanceover the entire element it is exposed for a long enough period to thevapors of ammonium polysulphide. Ifpnly portions are desired to be oflow resistance then only those portions are so exposed. Any

resistance range can thus be obtained; that is, from several megohms toa fraction of an ohm, dependent up on the degree of conversion of thecuprous oxide to cuprous sulphide. The sulphide surface has a bluecolor.

Ihave found that for higher mechanical strength instead of pure copper,the base for forming the oxide is composed of copper having a smallpercentage of another element. Bases composed of such alloys as 99.5%copper and 5% nickel; 99.8% copper and .2% silver or 99.5% copper and.5% aluminum are stronger than those having a pure copper base. As thealloyed elements are oxidized the alloying metal also is oxidized andlater sulphided. In these alloys the oxide is more dense and thecrystals are smaller and are of higher specific resistance.

What I claim is:

.1. A thermally formed resistance element for a variable resistancedevice having a condu'ctive metal oxide forits lower sector and an uppersector integrally formed therewith, said upper sector being a thermallyformed lower resistance compound of the mother metal of said lowersector oxide, the resistance of said element varying along its length inapproximate proportion to the depth of said upper sector.

2. A variable resistance device comprising a base composed substantiallyof a metal oxide, a varying depth surface layerof which has beenconverted to a compound of the mother metal of said base having a lowerresistance than said base, said surface layer approximately varying inresistance in proportion to its depth, and a contact member adapted tomake selective electrical connection with said variable resistancesurface along its length.

3. A variable resistance device comprising 'a base composedsubstantially of a metal oxide having an integral surface layer of lowerresistance of a compound of the mother metal, of said base, said layervarying in resistance along the length of said resistance element and acontact member adapted to make selective electrical connection with saidvariable resistance surface along its length;

7 4. A variable resistance device comprising a base composedsubstantially of an electrically conductive metal oxide and a layer of alower resistance compound formed from and on the surface of said baseand integral therewith, said layer being a compound of the mother metalof said base and an element of the oxy en series of the sixth periodicgroups, sai layer varying in specific resistance along the length ofsaid resistance element, and a movable contact member mountid to passover said variable resistance surace.

5. A variable resistance device comprising a base containing cuprousoxide having an integrally formed layer of a more conductive compound ofcopper on the contacting surface, said layer varying in specificresistance along the length of said resistance element, and a movablecontact member mounted to pass over said variable resistance surface.

'6. A variable resistance device comprising a base consistingsubstantially of copper oxide and an oxide of one or more metals otherthan copper, said base having an integrally formed layer of moreconductive compounds of the same metals on the contacting surface*varying in specific resistance along the length of said resistanceelement, and a movable contact membermounted to pass over said variableresistance surface.

7. In a rheostat a resistanceelement composed of a copper oxide'basehaving a layer of a compound of copper and an element of the sulphurgroup, other than-oxygen.

8. In arheostat a resistance' element comprising a base contalningcuprous oxide and I having an outer layer of a compound of copper and anelement of the sulphur group, other than oxygen, of varying thickness,

9. In a r eostat a resistance element coinprising a base containingcuprous oxide and having a copper sulphide layer thereupon varying inthickness inversely with the thickness of the base metal at any givensection of the element. v

10. In a rheostat a resistance element comprising a base composed ofcopper oxide and less than one percent. of an oxide of a metal having ahigher specific resistance than copper, and having a layer of a compoundof copper and an element of the sulphur series, other than oxygen.

11. In a rheostat a resistance element comprising a base containingcuprous'oxide and less than one percent of an oxide of a metal having ahigher specific resistance than copper and having a layer of coppersulphide.

: 12. In a rheostat a resistance element comprising a base containingcuprous oxide and less than one percent of an oxide of a metal having ahigher specific resistance than copper, and having a layer of a compoundof copper and an element of the sulphur series of the sixth periodicgroup, other than oxygen, said layer varying in thickness along fghebase inversely with the thickness of the ase. v

13. A rheostat having a resistance element comprising a base containingcuprous oxide and having a layer of a compound of copper and an elementof the sulphur series of the sixth periodic group, other than oxygen.14. A rheostat having a resistance element comprising a basecontainingcuprous oxide and having a layer of a compound of copper and an elementof the sulphur series of the sixth periodic group, other than oxygen,said layer having a thickness varying in-' versely with the thickness ofthe base metal at any section of thebase metal.

In testimony whereof, SAMUEL RUBEN has signed his name to thisspecification this th day of October, 1932. v

' SAMUEL RUBEN.

